Section IV, 1918 [37] Trans. R.S.C. 



Notes on the Origin of Colerainite. 



By Eugene Poitevin. 



Presented by W. McInnes, F. R.S.C. 



(Read May Meeting, 1918.) 



In seeking an explanation of the conditions required for the 

 genesis of colerainite, which they had identified in the laboratory 

 as a new mineral species, the authors of Museum Bulletin No. 27 of the 

 Geological Survey^ Poitevin and Graham, were obliged to base their 

 conclusions on the evidences presented by a few specimens which 

 had been obtained on the dumps of the Standard and Union pits at 

 Black Lake, the mineral at the time not having been found in place. 



Investigations carried out both in the field and in the laboratory 

 upon the diopside, grossularite, and vesuvianite, which occur in the 

 same localities, had led to the theory that these minerals were in large 

 measure recrystallizations of materials which had been dissolved 

 from the invaded country rocks by the extremely acid and igneous 

 magmas, which furnished the materials of the veins representing the 

 final phases of the intrusive period. Owing to the close similarity 

 between the mineral associates of colerainite and those of diopside, 

 grossularite, and vesuvianite, it was assumed that all of these minerals 

 had originated under like conditions. It was, however, noted that 

 the pits from which the colerainite had been derived were asbestos 

 pits and, therefore, associated with dykes which had invaded a limeless 

 or nearly limeless region of country rocks. 



Since the original article bearing on this subject was written, 

 one of the authors, the present writer, has visited the localities in 

 which the colerainite is found; and observations made under more 

 favourable conditions and in the light of previous experience, while 

 adding confirmatory evidence to former views regarding the genesis 

 of diopside, grossularite, and vesuvianite, throw doubt upon the view 

 that the genesis of the colerainite was similar. 



Colerainite was observed in place at the Union pit and at one 

 other pit in the vicinity, and in both instances it was found to be con- 

 fined to those portions of the dykes subject to the action of surface 

 waters. With the colerainite there were found associated in the 



Contributions to the mineralogy of the Black Lake area, Dept. of Mines, 

 Geological Survey, Museum Bulletin No. 27. 



